SYMPTOMS AND SIGNS

Typical
symptoms of powdery mildew include russeting on almond hulls. The symptoms are
reminiscent of rusty spot on peach fruit caused by Podosphaera leucotricha but without the typical powdery white
growth. No conidia (asexual spores) or chasmothecia (sexual fruiting structures
of powdery mildew fungi) are generally observed on the fruit. Foliar and twig
symptoms are absent.

COMMENTS ON THE DISEASE

Powdery mildew of almond has been only rarely
reported in California and generally does not cause economic crop losses. Other
crops such as peach have been reported to develop powdery mildew symptoms on
fruit without reproductive structures forming in the infected areas. Podosphaera leucotricha, P. tridactyla, and Podosphaera (=Sphaerotheca) pannosa have
been described on almond in California, as well as in other locations in the
world. Growth of the pathogen is favored by cool, moist nights and warm days.
Generally, fruit are susceptible only up to time of shell hardening, but later
infections can occur on some varieties. Certain cultivars such as Mission,
Padre, and Ruby are most susceptible.

MANAGEMENT

The
disease is rarely an economic problem on almonds in California. If management
of powdery mildew on almonds is needed, control practices should focus on
protecting fruit from infections. Jacket-split (late petal fall) and mid-spring
applications of powdery mildew fungicides are highly effective in managing the
disease. Avoid growing almonds near apple varieties that are highly susceptible
to powdery mildew, such as Jonathan, Gravenstein, and Rome Beauty. If nearby
apples are expected to cause mildew problems on almonds, control the disease on
apples.

Organically Acceptable Methods

Some
sulfur sprays are acceptable for use in an organically certified crop.

Chemical Control

Generally,
chemical control is not needed. If necessary, apply one of the fungicides
listed below from jacket split until mid-April.

COMMENTS:
Do not make more than two successive applications, and no more than 4 per season, to limit the development of resistance.

H.

SULFUR DUST#

Label rates

See label

0

MODE
OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)

COMMENTS:
Do not apply within 3 weeks of an oil application. Check with your certifier to determine which products are organically acceptable.

I.

WETTABLE SULFUR#

Label rates

See label

0

MODE
OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)

COMMENTS:
Do not apply within 3 weeks of an oil application. Check with your certifier to determine which products are organically acceptable.

J.

WETTABLE SULFUR#

See label

0

. . . PLUS . . .

LIQUID LIME SULFUR#

Label rates

See label

0

MODE
OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)

COMMENTS:
Do not apply within 3 weeks of an oil application. Check with your certifier to determine which products are organically acceptable.

+

Restricted
entry interval (R.E.I.) is the number of hours (unless otherwise noted) from
treatment until the treated area can be safely entered without protective
clothing. Preharvest interval (P.H.I.) is the number of days from treatment
to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.

#

Acceptable for use on organically grown produce.

1

Group
numbers are assigned by the Fungicide Resistance Action Committee (FRAC)
according to different modes of actions (For more information, see
www.frac.info). Fungicides with a different group number are suitable to
alternate in a resistance management program. In California, make no more
than one application of fungicides with mode of action Group numbers 1, 4, 9,
11, or 17 before rotating to a fungicide with a different mode of action
Group number; for fungicides with other Group numbers, make no more than two
consecutive applications before rotating to fungicide with a different mode of action Group number.

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